diff --git a/tests/checks/CodeCheckTestBase.php b/tests/checks/CodeCheckTestBase.php
index 6f316ee..7680529 100644
--- a/tests/checks/CodeCheckTestBase.php
+++ b/tests/checks/CodeCheckTestBase.php
@@ -15,7 +15,7 @@ protected function checkFile( $filename ) {
 			$file = array( new AnalyzedPhpFile( $filename, $file['php'][0] ) );
 		}
 
-		$this->assertFalse( $this->check->check( $file ) );
+		$this->check->check( $file );
 		return $this->check->get_errors();
 	}
 
diff --git a/tests/checks/test-BatcacheVariantCheck.php b/tests/checks/test-BatcacheVariantCheck.php
new file mode 100644
index 0000000..91b6efd
--- /dev/null
+++ b/tests/checks/test-BatcacheVariantCheck.php
@@ -0,0 +1,19 @@
+<?php
+
+require_once( 'CodeCheckTestBase.php' );
+
+class BatcacheVariantTest extends CodeCheckTestBase {
+
+	public function testBatcacheVariant() {
+		$actual_errors = $this->checkFile( 'BatcacheVariantTest1.inc' );
+		$error_slug = wp_list_pluck( $actual_errors, 'slug' );
+		$this->assertContains( 'batcache-variant-error', $error_slug );
+	}
+
+	public function testBatcacheVariantPositive() {
+		$actual_errors = $this->checkFile( 'BatcacheVariantTest2.inc' );
+		$error_slug = wp_list_pluck( $actual_errors, 'slug' );
+		$this->assertNotContains( 'batcache-variant-error', $error_slug );
+	}
+
+}
diff --git a/tests/data/BatcacheVariantTest1.inc b/tests/data/BatcacheVariantTest1.inc
new file mode 100644
index 0000000..22e4fd3
--- /dev/null
+++ b/tests/data/BatcacheVariantTest1.inc
@@ -0,0 +1,7 @@
+<?php
+function is_dangerous() {
+    if ( function_exists( 'vary_cache_on_function' ) ) {
+		vary_cache_on_function(	'require_once("something_dangerous.php");' );
+    }
+    return require_once("something_dangerous.php");
+}
diff --git a/tests/data/BatcacheVariantTest2.inc b/tests/data/BatcacheVariantTest2.inc
new file mode 100644
index 0000000..5a766df
--- /dev/null
+++ b/tests/data/BatcacheVariantTest2.inc
@@ -0,0 +1,10 @@
+<?php
+// there should be no error for the following
+function is_feedburner() {
+    if ( function_exists( 'vary_cache_on_function' ) ) {
+        vary_cache_on_function(
+            'return (bool) preg_match("/feedburner|feedvalidator/i", $_SERVER["HTTP_USER_AGENT"]);'
+        );
+    }
+    return (bool) preg_match("/feedburner|feedvalidator/i", $_SERVER["HTTP_USER_AGENT"]);
+}
diff --git a/vip-scanner/checks/BatcacheVariantCheck.php b/vip-scanner/checks/BatcacheVariantCheck.php
new file mode 100644
index 0000000..90d6511
--- /dev/null
+++ b/vip-scanner/checks/BatcacheVariantCheck.php
@@ -0,0 +1,37 @@
+<?php
+/*
+ * Checks for invalid batcache variant function vary_cache_on_function() that:
+ * - includes dangerous illegal functions
+ * - does not reference superglobal variable
+ */
+
+class BatcacheVariantCheck extends CodeCheck {
+
+	function __construct() {
+		parent::__construct( array(
+			'PhpParser\Node\Expr\FuncCall' => function( $node ) {
+				$name = $node->name->toString();
+				if ( 'vary_cache_on_function' == $name ) {
+					$value = $node->args[0]->value;
+					if ( $value instanceof PhpParser\Node\Scalar\String )  {
+						$function_string = $value->value;
+						if ( preg_match('/include|require|echo|print|dump|export|open|sock|unlink|`|eval/i', $function_string, $matches) ) {
+							$this->add_error(
+								'batcache-variant-error',
+								'Illegal word "'.$matches[0].'" in variant determiner.',
+								BaseScanner::LEVEL_BLOCKER
+							);
+						}
+						if ( !preg_match('/\$_/', $function_string) ) {
+							$this->add_error(
+								'batcache-variant-error',
+								'Variant determiner should refer to at least one $_ superglobal.',
+								BaseScanner::LEVEL_BLOCKER
+							);
+						}
+					}
+				}
+			}
+		) );
+	}
+}
diff --git a/vip-scanner/config-vip-scanner.php b/vip-scanner/config-vip-scanner.php
index e9f688b..86ff0bc 100644
--- a/vip-scanner/config-vip-scanner.php
+++ b/vip-scanner/config-vip-scanner.php
@@ -11,6 +11,7 @@
 
 VIP_Scanner::get_instance()->register_review( 'WP.com Theme Review', array(
 	'AtPackageCheck',
+	'BatcacheVariantCheck',
 	'BodyClassCheck',
 	'CDNCheck',
 	'CheckedSelectedDisabledCheck',
@@ -54,6 +55,7 @@
 ) );
 
 VIP_Scanner::get_instance()->register_review( 'VIP Theme Review', array(
+	'BatcacheVariantCheck',
 	'CheckedSelectedDisabledCheck',
 	'DeprecatedConstantsCheck',
 	'DeprecatedFunctionsCheck',